1. Field of the Invention
The invention relates to an all pressure switch. More specifically, the invention relates to such a switch which includes a housing member having a recessed well for holding a degassed, non-compressible, electrically insulating fluid spacer.
The invention also relates to a control module including such all pressure switches.
The invention also relates to a process for making such all pressure switches.
2. Description of Prior Art
It is known in the prior art to provide switches, or other like devices, having spacers made of a liquid or other fluid or a solid material. Such switches or other devices are described in the following patents: U.S. Pat. No. 4,017,848, Tannas, Jr., Apr. 12, 1977; U.S. Pat. No. 3,784,768, Hunt, Jan. 8, 1974; IBM Technical Disclosure Bulletin, Vol. 14, No. 8, Jan. 1972; U.S. Pat. No. 4,524,256, Miyata et al, June 18, 1985; U.S. Pat. No. 2,487,433, Gardenhour, Nov. 8, 1949; U.S. Pat. No. 4,689,879, Fowler, Sept. 1, 1987; French Patent No. 2,370,348, Leveille, June 1978; U.S. Pat. No. 4,109,118, Kley, Aug. 22, 1978; WO 81/00787, Marshall, Mar. 19, 1981; U.S. Pat. No. 3,864,024, Olson, Feb. 4, 1975; IBM Technical Disclosure Bulletin, Vol. 13, No. 3, Aug. 1970; U.S. Pat. No. 4,421,958, Kameda, Dec. 20, 1983; U.S. Pat. No. 4,066,855, Zenk, Jan. 3, 1978; and U.S. Pat. No. 4,520,248, Woelfel, May 28, 1985.
The above references are discussed below:
In U.S. Pat. No. 4,017,848, a switch array comprises an upper electrode and a lower electrode separated from each other by a transparent dielectric fluid. The electrodes are also transparent so that a legend can underlie the switch. As the switch operates at atmospheric pressure, there is no teaching of using a degassed fluid.
In U.S. Pat. No. 3,784,768, a submersible touch operated signaler includes a front plate and a rear plate--both of which are of a conductive material and grounded--and an intermediate plate--also of a conductive material and connected to a source of low voltage. The plates are spaced from each other and the entire arrangement is submersible in, for example, a swimming pool. When submersed, water from the pool flows into the regions between the plates (see column 4, lines 10 et seq. of the patent).
In IBM Technical Disclosure Bulletin, Vol. 14, No. 8, January 1972, a hydraulically controlled keyboard comprises fluid chambers 2 underlying switch actuator 6 housing. The chambers are connected by a channel 3. Fluid is contained in the chambers and channel. As the switch mechanism is disposed in the switch actuator housing, the fluid does not need to be an insulating fluid. As the mechanism is operated at atmospheric pressure, the fluid does not have to be degassed.
In U.S. Pat. No. 4,524,256, a pressure sensitive switch comprises a conductive porous material spaced from a conductive layer by an elastic insulator. The elastic insulator not being a fluid, the switch of the plastic does not include an insulating, degassed fluid spacer.
In U.S. Pat. No. 2,487,433, a ball contactor switch comprises a conductive ball 23 in a fluid filled tubular container 10. There are, of course, substantive differences between the present invention and the teaching of this patent.
In U.S. Pat. No. 4,689,879, a membrane keyboard has two circuit layers with spacers disposed between them. Vents are provided to permit the escape of trapped air.
In French Patent 2,370,348, a keyboard for a pocket calculator includes a flexible foil 18 having conductive discs. The flexible foil is spaced from a set of broken paths 15 by a compressible fluid 20.
In U.S. Pat. No. 4,109,118, there is taught an array of manually operable key switches in which each switch comprises a fluid filled bag under a key cap. The fluid does not have to be an insulator, nor is there any teaching in the patent that the fluid be degassed.
In WO 81/00787, a switch structure uses, e.g., a displaceable fluid to provide a degree of resilient resistance.
In U.S. Pat. No. 3,864,024, an optical display device includes a transparent layer 1, an overlying layer 2 and a liquid 3 between layers 1 and 2.
In IBM Technical Disclosure Bulletin, Vol. 13, No. 3, August 1970, a switch has a conductive strip 12 mounted on a substrate 10. A cover 14 overlies the substrate and includes a metallic contact 14B. A liquid 20 separates 12 from 14B. There is no teaching of degassing the fluid.
In U.S. Pat. No. 4,421,958, a membrane switch includes conductive layers 1 and 5 which are mounted on substrates 2 and 6 respectively and are separated by air. The substrates are spaced by a porous sheet 12 so that air can be brought into and discharged from the space between the conductive layers.
In U.S. Pat. No. 4,066,855, there is taught a vented membrane switch. It uses the same principles as the '958 patent except that there is provided a vent in the main membrane to permit airflow.
In U.S. Pat. No. 4,520,248, a keyboard assembly includes conductive strips 20 and 28 which are spaced by an insulating strip 22.
The prior art also teaches degassing machines as illustrated in U.S. Pat. Nos. 2,413,102, 2,485,857 and 3,154,087.
With respect to switches having fluid spacers, if there is gas in the fluid, then the switches will have difficulties at either extreme of pressure, i.e, at high pressures or at low pressures. At high pressures, the gas will be compressed so that contact may be made when it is not desired. At low pressures, the gas will expand making the switch difficult to operate or possibly even bursting the switch depending on the amount of gas in the fluid.